Particle counting apparatus



April 30, 1963 CATHODE RAY TUBE

D. S. HOBBS a s i6 a PHOTO- ELE CTRIC CELL 2 7 DEFLEOTION AMPLIFIER cmcurrs B SHAPING CIRCUIT DELAY DELAY GOINGIDENCE LINE LINE CIRCUIT DELAY L A COUNTER LINE ATE GATE 1 i z 12 k msTADLE/ CIRCUIT V 1 RESET H cmcun' TIMING i INTERGEPT SELECTOR GATE J"' Fl G2 b .1 c 2 F 3 drsTd\ 4 5 INVENTOR Dona/J Sydn H 55 AGENT United States Patent Filed May 27, 1957, Ser. No. 661,807 Claims priority, application Great Britain May 17,

Claims. (Cl. 250-417) The invention relates to particle counting and sizing apparatus of the kind in which a particle sample is scanned in a series of parallel lines by a flying spot scanner, which may be of the cathode ray tube type, electrical slgnals being produced by a photo-electric cell corresponding to interceptions of the particles by the flying spot and in which a line to line memory device is provided to rememher the interceptions of particles in one line of scan until the succeeding line is scanned.

With such apparatus it is possible to derive a total count of the number of particles in the sample even if they are of widely different sizes since the line-by-line memory device enables all interceptions except the first (or last) of a large particle overlapping two or more lines of scan to be disregarded so that such a particle is counted only once.

In order to obtain sizing counts of the particles, that is to say, counts of the particles in each of a number of size groups, various methods have already been proposed, for example, when a particle is first (or last) seen, the scanning spot is arrested and caused to examine the particle before continuing its normal scanning motion.

The object of the invention is to provide alternative means for providing sizing counts of the particles in a sample and with this object in view and according to the invention a particle counting apparatus of the kind first above referred to comprises a delay system having a transit time shorter than the scanning line period for reproducing the signal due to the first interception of a particle overlapping more than one line, or a regeneration of such signal, during succeeding interceptions of the particle, means for comparing the duration of each such interceptions with a predetermined time interval and means for routing a count signal to a counter when the signal duration is greater than the said time interval.

Other features of the invention will be apparent from the following description of one embodiment which is given by way of example only, with reference to the drawing in which FIGURE 1 shows in block schematic form the circuit arrangement of a particle counter according to the invention, and FIGURE 2 is a diagram of "a portion of a particle sample showing one (large) particle intercepted by the scanning lines.

In FIGURE 1 the flying spot scanner includes a cathode ray tube 1 with associated deflection circuits 2 for causing the cathode ray beam to trace out a rectangular raster on the fluorescent screen. A lens or lens system 3 focuses the image of the flying spot on the specimen 4 and a further optical system 5 directs the light passing through the sample into a photo-electric cell 6. The output of the cell 6 is amplified by amplifier 7 and the amplified signals pass through a shaping circuit 8 to a coincidence circuit 9 and to a delay line 14. This delay line may be for example of the magneto-striction type and have 'a delay time 6T which is a small fraction of the scanning line period T. Delay lines of this type are disclosed, for example, in the article Ultrasonic Metal Delay Lines, Tele-Tech and Electronic Industries, March 1954, at pages 78, 178-9. The output from this delay line is passed to a further delay line 15 which again may be of the magneto-striction type and provides a delay equal to T-6T. The output from the delay line 15 which is eiiectively the output from the shaper 8 delayed by time T is supplied to the coincidence circuit 9 which provides a pulse output on the first interception of a particle by the scanning spot but has no output whenever there is coincidence between the signal from the particle being scanned and the delayed signal representing the scanning of the same particle in the preceding line.

In order to provide sizing counts of particles in a sample the count pulse produced at point a, FIGURE 2, by the coincidence circuit is passed through a delay line 16, which may also be of the same type as delay line 14, and which has a delay time T6T which is slightly less than the scanning line period T so that this pulse emerges from the device 16 at point b" in the next line (2) of scan. This emergent pulse is passed to a bi-stable circuit 1t) which it triggers into one stable state. At the end of the particle intercept at point c the video signal from the shaper circuit 8 resets the bistable circuit 10 through the medium of re-set circuit 11. As the bistable circuit 10 re-sets, it produces a pulse similar to the pulse emitted by the coincidence circuit 9. This pulse is recirculated through gate 18, gate 17 and delay line 16 and again triggers the bistable circuit 10 when the scanning spot has reached point d in scanning line 3. A further pulse is produced from the bistable circuit when the line 3 intercepts terminates at e and this process of pulse circulation and regeneration continues down to the exit edge of the particle until point f is reached. The pulse delayed from point f appears at point g in line 7 but the bistable circuit is held re-set by the video signal from the shaper circuit 8 since there is no particle intercept present. Thus re-circulation of the pulses cannot continue.

It will be clear from this that the original count pulse generated at point a by the coincidence circuit 9 is carried through the memory system and is regenerated at the end of each intercept of the particle. Re-circulation of the pulse may be stopped at the end of any intercept by a simple gate, for example gate 18 following the bistable circuit 10. If now each intercept is sampled for length, for example by a timing circuit which is initiated at the commencement of each intercept and produces a voltage step signal after a predetermined period then it can be arranged that if the step is produced within the intercept the pulse re-circulation can be stopped and a count pulse routed to the counter 12.

This arrangement is shown in FIGURE 1 by the provision of the timing intercept selector 13 to the input of which is supplied the video signal from the shaper circuit 8. A timing intercept selector of the type which may be employed for the selector 13 is disclosed, for example, in Waveforms (volume 19 of the Radiation Laboratory Series), McGraw-Hill, 1949, on pages 367 and 369, partic ularly the circuit of FIG. 10.5. The output from the selector 13 is taken to gate 18 and also to gate 19 which opens when gate 18 closes. Thus with the timing period of the selector 13 set to "a known length (having regard to the speed of scan) a count pulse will only be sent to the counter through gate 19 from bistable circuit 10 by those particles with an intercept greater than the set length. As above described when gate 18 closes the recirculation of the pulse from the bistable circuit 10 is prevented so that although there may be further interceptions of a particle by the scanning beam after the count has taken place there is no further operation of delay 16 or counter 12 by these interceptions.

By successively varying in steps the period of the timing circuit 13, sizing of the particles in a sample can be achieved because at each setting a count is taken of all those particles with intercept-s greater than the setting.

In order to obtain a total count of the particles in a sample irrespective of their sizes the output from the coincidence circuit 9 may be directed by manual switch S direct to the counter 12. Switch 5; is ganged with switch S which isolates the output of gate 19 from the counter 12.

The gates'17-19, the bistable and reset circuits and 11, the counter 12, and the coincidence circuit 9 may be any conventional circuits for performing the required function. For example, the gate 17 may be of the type disclosed on page 380, FIG. 10.17 of Waveforms (vol. 19 of the Radiation Laboratory Series), McGraw-Hill, 1949. The bistable and reset circuits 10 and 11 may comprise a conventional flip-flop circuit, such as shown on page 187, FIG. 5.36 of the above-cited book Waveforms, with two inputs being provided in the manner shown in Digital Computer Components and Circuits, R.K. Richards, D. Van Nostrand Co., Inc., 1957, on page 71, FIG. 3.3. The gate circuit 18 may comprise a flipflop of the type employed for the circuits 10 and 11, with a pair of gates of the type of gate 17. In the circuit 18, the flip-flop may be connected to open one gate in response to pulses from circuit 10 in order to pass pulses from circuit 10 to gate 17, and to close the one gate and open the other gate in response to pulses from selector 13. The other gate is connected. to pass pulses from the gate 19.

The gate circuit 19 may comprise a flip-flop of the above-noted type, the flip-flop being responsive to signals from theselector '13 and gate 18 to provide a signal for opening a gate'of the type employed for gate 17. This latter gatemay be connected to pass pulses from the circuit;10 to the counter 12. The counter 12 may be a scale-of-ten counter, for example, as shown on page 611, FIG. 17.8, of the above-cited book Waveforms.

The coincidence circuit 9 may also comprise a flip-flop circuit of the above-noted type. In this circuit, one input may be provided by an AND circuit, as shown on page 38, FIG. 2.1(a) of the above-cited book Digital Computer Components and Circuits, the AND circuit being connected to provide an output when signals from the shaping circuit 8 and the delay circuit coincide. The other input to the flip-flop circuit may be derived from the trailing edges of pulses from the shaping circuit 8, for example, by differentiation in an R-C differentiating network. The flip-flop may be employed to control a gate of the type of gate 17, for passing the trailing edge pulse.

Although the operation of the circuit has been described with reference to only one particle it will be clear that the same operations will occur with every particle intercepted in the scanning lines.

What is claimed is:

1. Particle counting apparatus comprising scanning means for scanning a particle in successive lines, detecting means connected to detect scanning interceptions of said particle, circuit means connected to said detecting means for generating a signal indicative of the time required to scan the area of said particle, said circuit means comprising a signal feedback path including a delay line having a transit time shorter than a line scanning period and means to feed a signal through said feedback path each time said particle is intercepted during successive line scansions, comparison means connected to compare the duration of said signal with a predetermined time interval, and means for counting said signal when the duration thereof is greater than said predetermined time interval.

2. Particle counting apparatus comprising scanning means for scanning a particle in successive lines, detecting means connected to detect scanning interceptions of said particle, circuit means connected to said detecting means for generating a signal indicative of the time re- .quired to scan the area of said particle, said circuit means comprising a signal feedback path including a delay line having a transit time shorter than a line scanning period and means to feed a signal through said feedback path each time said particle is intercepted during successive line scansions, comparison means connected to compare the duration of said signal with a predetermined time interval, means for counting said signal when the duration thereof is greater than said predetermined time interval, and a line to line memory device connected to said detecting means for causing only the first scanning interception of a particle to reach said circuit means.

'3. Apparatus as claimed in claim 2, in which said line-to-line memory device comprises a second delay line having a transit time equal to a line scanning period,

' a coincidence circuit, means connecting the output of said detecting means to an input of said coincidence circuit, and means connecting said output of the detecting means to another input of said coincidence circuit via said second delay line.

4. Apparatus as claimed in claim 2, in which said comparison means comprises a timing circuit connected to start a timing cycle upon the occurrence of said first scanning interception and adapted to produce a timed pulse after a predetermined time interval, a counter, and a gate circuit connected to permit said signal to reach said counter in response to the occurrence of said timed pulse.

5. Apparatus as claimed in claim 4, including means connected to said timing circuit for varying said predetermined time interval thereby to permit counting of pulses of different sizes.

References Cited in the file of this patent UNITED STATES PATENTS 2,494,441 Hillier Jan. 10, 1950 2,789,765 Gillings Apr. 23, 1957 2,791,377 Dell et a1. May 7, 1957 2,791,695 Bareford et a1 May 7, 1957 2,803,406 Nuttall Aug. 20, 1957 2,891,722 Nuttall June 23, 1959 2,927,219 Young et al Mar. 1, 1960 FOREIGN PATENTS 739,902 Great Britain Nov. 2, 1955 

1. PARTICLE COUNTING APPARATUS COMPRISING SCANNING MEANS FOR SCANNING A PARTICLE IN SUCCESSIVE LINES, DETECTING MEANS CONNECTED TO DETECT SCANNING INTERCEPTIONS OF SAID PARTICLE, CIRCUIT MEANS CONNECTED TO SAID DETECTING MEANS FOR GENERATING A SIGNAL INDICATIVE OF THE TIME REQUIRED TO SCAN THE AREA OF SAID PARTICLE, SAID CIRCUIT MEANS COMPRISING A SIGNAL FEEDBACK PATH INCLUDING A DELAY LINE HAVING A TRANSIT TIME SHORTER THAN A LINE SCANNING PERIOD AND MEANS TO FEED A SIGNAL THROUGH SAID FEEDBACK PATH EACH TIME SAID PARTICLE IS INTERCEPTED DURING SUCCESSIVE LINE SCANSIONS, COMPARISION MEANS CONNECTED TO COMPARE THE DURATION OF SAID SIGNAL WITH A PREDETERMINED TIME INTERVAL, AND MEANS FOR COUNTING SAID SIGNAL WHEN THE DURATION THEREOF IS GREATER THAN SAID PREDETERMINED TIME INTERVAL. 